Detecting fluorescence via CW or pulsed LEDs

[Anton Alice]

Hello forums,

in the context of a little DIY-project I am planning to build a rudimentary fluorometer, which is actually doing nothing but checking whether an amount of protein is fluorescing or not, and roughly measuring its intensity.

A highpower LED is used to excite the protein to the fluorescent state, while a phototransistor (specially sensitive to the fluorescent spectrum) starts measuring a short time after the LED has been turned off.
The live time of fluorescence is in the region of a few nano seconds. For example a nanosecond pulsed measurement should (tightly) be able to solve the problem. Do you know circuitries which can handle this measurement cycle?

 

[Anton Alice]

I know its difficult.

For the continuous approach:
How well can optical filters block light? What is the best possible attenuation (below 200dollars)?

 

[berkeman]

The live time of fluorescence is in the region of a few nano seconds.

Why is the time constant so short? What is the fluorescing material?

 

[Anton Alice]

One can distinguish between fast and slow decaying luminscence. The fastest kind of luminescence is fluorescence. There is also phosphorescence, which is more of an "exite, and wait until it decays", whereas fluorescence is more of a direct conversion of one wavelength to another.
http://nic.ucsf.edu/FPvisualization/#ref30
http://nic.ucsf.edu/FPvisualization/#ref30

Fluorescence is always in the nanosecond region.